Electrical drop cord switch operated by removable key



Aug. 5, 1958 e. WINTRISS 2,846,530

ELECTRICAL DROP CORD SWITCH OPERATED BY REMOVABLE KEY Filed OCt. 25, 1954 2 Sheets-Sheet 1 Aug. 5, 1958 s. WINTRISS 2,

ELECTRICAL naop com: swITcH OPERATED BY REMOVABLE KEY Filed Oct. 25, 1954 2 Sheet-Sheet 2 I I ,r "f x w Q 90 IN VEN TOR.

AT ran'lvsxs United States Patent ELECTRIQAL DROP CORD SWITCH OPERATED BY REMOVABLE KEY George Wintriss, Carversville, Pa.

Application October 25, 1954, Serial No. 464,217

7 Claims. (Cl. 200-42) This invention relates to a safety switch for preventing the unauthorized use of electrical equipment. The switch is located in the drop cord of the electrical equipment and is intended primarily for preventing children from plugging in power tools or kitchen appliances where the operation of the apparatus would be dangerous to the child. It can also be used for preventing children from using radios and television sets without permission.

It is an object of the invention to provide an improved, key-operated switch for use in the drop cord circuit of an electrical appliance. In the preferred construction of the invention, the switch is located in an auxiliary plug which is permanently connected to the conventional plug at the end of the drop cord. In one modification of the invention, the improved switch is connected directly to the end of the drop cord and comprises the only plug at the end of the drop cord. In still another modification the switch is located at an intermediate location between the ends of the drop cord.

Another object of the invention is to provide a simple and inexpensive electric switch that can be closed only with a particular key for which the switch is designed. Another object is to provide a switch, of the character indicated, in which the key itself comprises a part of the circuit when the switch is closed.

Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds.

In the drawing, forming a part hereof, in which like reference characters indicate corresponding parts in all the views;

Figure 1 is a sectional view of a switch made in accordance with this invention and shown connected to a conventional drop cord plug, the section being taken on the line 11 of Figure 2;

Figure 2 is a sectional view taken on the line 22 of Figure 1;

Figure 3 is a fragmentary view showing a modified construction of one end of the switch shown in Figure 1;

Figure 4 is a sectional view showing another modified form of the invention;

Figures 5-7 are views of the key, as seen from different sides, for operating the switches shown in the other views; and

Figures 8 and 9 are sectional views showing another modification of the invention with the parts in different positions in the different figures.

Figure 1 shows a plug 10- at one end of a drop cord 11. This plug has the usual prongs 13 for insertion into a base board outlet or into any other suitable sockets for receiving such prongs. This type of plug is in universal use for drop cords operating from single phase power. The invention shown in Figure 1 comprises an auxiliary plug 15 having prongs 16 and 17 which are at the same spacing as the prongs 13 of the conventional drop cord plug.

The prong 16 is securely anchored in the left hand portion of the auxiliary plug 15, the body of the plug being molded around the anchored portion of the prong in accordance with conventional practice for equipment of this kind.

The body of the plug 15 comprises a housing 18 with chambers therein for conductors and contacts, as will be described. The prong 16 connects at its inner end with a conductor 20 located in a chamber 22 in the housing 18. This conductor 20 is preferably of one piece construction with the prong 16.

At the end of the housing 18, remote from the prongs 16 and 17, there are openings for receiving the prongs 13 of the plug 19. One of the prongs 13 extends into the chamber 22; and the conductor 20 is bent back on itself so as to have a resilient end portion which extends along the inner side of the prong 13.

The conductor 20 has a projecting end portion 24, which engages in an opening 25 in the prong 13. When the prong 13 is initially inserted into the auxiliary plug 15 far enough for the projecting end 24 to snap into the opening 25 in the prong 13, the plug 10 is permanently attached to the auxiliary plug 15 because there is no provision for ever removing the projecting end portion 24 from the opening 25.

The prong 17 is anchored in the body portion of the auxiliary plug 15, and there is a contact 26 at the inner end of the prongs 17 and preferably of one piece construction therewith. This contact 26 is located at one side of a chamber 27 within the body of the auxiliary plug 15. On the other side of the chamber 27 there is another contact 29 which is resilient and which has a depression 30 extending across it transversely for receiving a conductor element of a switch key which bridges the space between the contacts 26 and 29 when the switch is closed.

The location of the conductor element for closing the switch is indicated in dotted lines in Figure 1 and the conductor element, is designated by the reference character 33, but. the actual construction will be explained more fully in connection with Figures 57. In connection with the resilient conductor 29, however, it should be understood that the purpose of the depression 3%! is to hold the conductor element 33 in position when it is in the location indicated by dotted lines, and that the depression 30 has a sloping side Wall so that the conductor element 33 can move out of the depression when rotated about its center in a clockwise direction in Figure 1.

The contact 29 is connected with a conductor 35 located in a chamber 36 in the housing 18 of the auxiliary plug 15. This conductor 35 is preferably of one piece construction with the contact 36 and is of the same shape as the conductor 29 with a projecting end 24 which engages in an opening 25 in the other prong 13 of the plug Iii.

There is a key hole 40 opening through one side of the housing 18 for providing access to the chamber 27. In the preferred construction, the key hole 43 does not extend all the way through the housing but has an end wall 42 (Figure 2) for limiting the extent to which a key can be inserted into the key hole.

Figures 5-7 show a key 45 for use with the auxiliary plug 15 of Figures 1 and 2. This key 45 has a shank 47 with a handle 48 at one end. There is a hole 49 in the handle 48 for hanging the key on a hook or key ring, or for receiving a cord or other connection for a key tag. At the other end of the shank 47 there is the conductor element 33 with portions projecting from opposite sides of the shank 47. The shank 47 is preferably made from insulating material, but the shank can be made of metal if the handle 48 is of insulating material. It is not desirable to have the entire key 15 made of metal unless the construction of the invention is modi- 3 fied to make the key serve merely as an actuator for the switch and not as a part of the circuit of the switch.

In the preferred construction of the invention, the ends of the conductor element 33 which project from opposite sides of the key shank 47 are offset from one another so as to make it more difficult to operate the switch with a hairpin or other makeshift key. The chamber 27 in the housing 18 is also offset in the same manner as the projecting ends of the conductor element 33, and this construction is best shown in Figure 2. The auxiliary plug 15 is preferably made in two halves, each of which is molded in accordance with conventional practice for drop cord switches such as are used on electric iron cords.

Instead of connecting the two halves of the auxiliary plug body together with bolts, the halves are preferably secured together by rivets 54 so that they cannot be separated by someone who wishes to remove the plugltl from its connection with the auxiliary plug 15.

The outstanding advantage of the construction shown in Figures 1 and 2 is that it can be .used with any drop cord having a conventionalplug at one end. In the manufacture of new equipment, however, there is no purpose in providing a conventional plug 10 and an auxiliary plug as shown in Figures 1 and 2. Instead of using such an assembly, the invention is modified as shown in Figure 3. The left hand end of the housing 18 is the same as in Figures 1 and 2, but in the chamber 22 there is a conductor 56 having a screw 58 for connecting the conductor to a wire 60 of the drop cord 11.

In the chamber 36 of the housing 16 there is a similar conductor 56 having a screw 58 for connecting another wire 62 of the drop cord to the conductor 56 in the chamber 36.

Figure 4' shows another modification of the invention for use at some location intermediate the ends of a drop cord. This modification of the invention includes a housing 70 with chambers 22 and 36 at its right hand end including conductors 56 for connection with the wires 60 and 62 of the drop cord 11, the construction being the same as in Figure 3.

At the other end of the housing 70 there are other chambers 71 and 72 corresponding to the chambers 22 and 36 and containing conductor-s 56 and screws 58 for connection to a portion of the wires 60 and 61 which lie beyond the housing 70. It will be understood that the housing 70 can be located at any convenient place along the drop cord 11 by merely cutting the drop cord at such a location and peeling back the insulation as necessary in order to make the connections shown in Figure 4.

Different models of the housing 18 can be made having offsets in the chamber 27 for fitting keys that have different offsets of the conductor element 33, or that have the conductor element 33 of different lengths.

Figure 8 shows another modification of the invention in which the key and contacts provide a snap action switch in the circuit.

In this modified form of the invention a housing 75 is provided with differently shaped chambers for obtaining longer and more resilient contact elements. The construction shown in Figures 8 and 9 is an auxiliary plug for permanent connection with a conventional plug, as in the construction shown in Figure 1. It will be understood, however, that the construction shown in Figures 8 and 9, for obtaining snap action, can also be used with modifications such as shown in Figures 3 and 4.

There are prongs 16 and 17 extending from the housing 75. The prong 16 extends into a chamber 77 in the housing 75 and connects with a conductor 80 which is preferably of one-piece construction with the prong 16. This conductor 80 is bowed so as to serve as a leaf spring, and it has a projection 82 struck from the body of the conductor 80 at a location to engage in a hole in the end of the prong 13 (Figure 1) when the prongs of the plug 10are inserted-into-the housing.

and connects with a conductor 86 which is preferably of one-piece construction with the prong 17. This conductor 86 is bent back on itself to provide a substantial resilience for movement of a contact 88 at the end of the conductor 86 and preferably of one-piece construction with the conductor.

Within the housing 75, there is another conductor 90 with a projection 92 displaced from the body of the conductor, in the same way as the projection 82, for engaging an opening in a conventional drop cord plug for permanently securing the drop cord plug to the housing in the manner already explained.

The contact 88 islocated below the keyhole 40 in Figure 8; and there is another contact 96 located above the keyhole 40 at one end of the conductor 90. This contact 96 is on a long portion of the conductor which can be displaced outwardly in a chamber 98 of the housing for obtaining substantial movement of the contact 96 with only a slight bending of the conductor 90.

One feature of the construction shown in Figures 8 and 9, which differs from those in the other views, is that the contacts 88 and 96 are at different distances from the axis of the keyhole 40. This requires a key 100 having conductor elements 102 and 103 which are of different length. The feature can also 'be used in the construction shown in the other views by constructing the invention with the contacts at different spacing fromthe axis of the keyhole. The construction shown in Figure 8 also includes the longitudinal offsetting of the contacts 88 and 96 and the contact elements 102 and 103 of the key in the same manner as in the other modifications already described in connection .with Figures l-7.

Figure 8 shows the key 100 in full lines in thepo'sition which it occupies when it is initially inserted into the keyhole 40. The contacts 88 and 96 are shown in full lines in the positions which they occupy when not displaced by the contacts 102 and 103 of the key. The conductors 86 and 90, of which the contacts 88 and 96 form the end portions, have a spring bias which holds them in contact with walls 106 and 107, respectively, of the chambers 84 and 98.

As the key 100 is turned clockwise, in Figure 8,

the conductor element 102 displaces the contact 96 and conductor 90 into the dotted line position shown in Figure 8. Continued rotation of the key 100 carries the contact element 102 into the position shown in Figure 9, the last part of this rotary movement of the key being impelled by the force of the conductor 98 hearing against the side of the conductor element 102 of the key.

During this final movement of the key 100 into the position shown in Figure 9, the conductor element 103 displaces the contact 88 and conductor 86 into the positions shown in Figure 9. The turning of the key is limited by the end wall 110, or can be limited by th up-turned end of the contact 88. V

When the key 100 is in the position shown in Figure 9, the conductor element 103 has its end face in a depression in the confronting face of the contact 88. When the key 100 is turned counter-clockwise to break the circuit of the switch, the contact 88 and conductor 86 are moved away from the axis of the key as the conductor element 103 passes out of the depression in the face of the contact 88. This bends the conductor 86 further away from the face 106 in the housing and imparts additional tension to the conductor 86.

As the turning of the key 100 is continued in. a counter-clockwise direction, the end of the conductor element 103 reaches the downwardly sloping portion of the conductor 86, and the conductor element 103 .then snaps away from the conductor 86 to break the circuit.

Further turning of the key counterclockwise, causes the contact 96 to come against the upper side of the conductor element 102 and a curved face 112 of the contact 96 serves as a cam for displacing the conductor element 102 angularly about the axis of the key.

The preferred embodiment and some modifications of the invention have been illustrated and described, but other modifications and changes can be made, and some features can be used in difierent combinations, without departing from the invention as defined in the claims.

What is claimed is:

1. An electrical switch comprising a housing having prongs projecting from one end thereof for insertion into an electrical outlet, the housing having openings in its other end at locations for receiving the prongs of a drop cord plug, conductors within the housing in position to engage the prongs of the drop cord plug when fully inserted into the housing, projections on the conductor in position to engage behind surfaces of the prongs of the drop cord plug for permanently locking the prongs of the drop cord plug in the housing, means connecting the conductors which engage the prongs of the drop cord plug with the corresponding prongs which extend from the other end of the switch housing, said means including a key-operated switch between at least one of the conductors and its corresponding prong of the switch housing, the housing having a key hole therein for admitting a key to the switch, and a key for the switch, the key being of a size for admission and removal through said keyhole.

'2. The electrical switch described in claim 1 and in which the means for locking the drop cord plug prongs in the switch housing comprise projecting ends on the conductors in position to engage in openings of the prongs of the drop cord plug, and in which the prongs of the drop cord plug and the conductors which engage them are located in chambers of the housing having side walls which prevent the engaged parts from bending away from one another and becoming disengaged when a pull is applied to the drop cord plug to separate it from the switch housing into which its prongs have been inserted.

3. An electrical switch including a housing, conductors in one end of the housing with means for connecting them with wires for leading to a source of power, conductors in the other end of the housing with fastening means for connecting to wires of a drop cord leading to an electrical appliance, spaced contacts within the housing on difierent sides of a chamber, the contacts being resilient and movable toward and from one another to change the space between them, one of the contacts being connected to a conductor at the power supply end of the housing and the other contact being connected to one of the conductors at the electrical appliance end of the housing, the housing having a key hole opening through at least one side thereof for admitting a key into the chamber between the contacts, and a key having a shank which extends through the key hole into the chamber and a conductor element extending from difierent sides of the shank and slightly longer than the normal spacing of the contacts from one another and adapted to simultaneously reach both of the spaced contacts in the chamber and spread them further apart to obtain pressure against the key when the key is turned into a predetermined angular position for closing the circuit between the spaced contacts, the keyhole being of a cross-section at least as great as that of the conductor portion of the key whereby the key can be inserted and removed through the keyhole, and the conductors have resilient spring means within the housing for causing the conductor elements of the key to engage and disengage the spaced contacts with a snap action.

4. An electrical switch assembly comprising a housing, conductors at one end of the housing for connection with the two sides of a power line, conductors at the other end of the housing for connection with the wires of a drop cord leading to an electrical appliance, and an electrical switch comprising contacts within the housing and spaced from .one another in a chamber of the housing, the contacts being resilient and movable toward and from one another to change the space between them, one of the contacts being connected with one of the conductors at the power line end of the switch, and the other contact being connected with the corresponding conductor at the other end of the switch housing, the housing having a key hole opening into the chamber at a location close to the switch,

and a removable key which extends through the key holev and into the chamber, the key having a conductor at its inner end extending from a shank of the key and movable into position to bridge the space between the contacts in said chamber when the key is rotated after being inserted through the key hole, the conductor being of a size which passes through the keyhole whereby the key can be inserted into the housing and removed, at least one of the contacts being resilient and having a depression therein on one side thereof, the depression having a sloping wall, and the conductor of the removable key engaging in the depression in the resilient contact of the switch for holding the shank against rotation when the key is in position to close the switch.

5. An electrical switch assembly comprising a housing, conductors at one end of the housing for connection with the two sides of a power line, conductors at the other end of the housing for connection with the wires of a drop cord leading to an electrical appliance, and an electrical switch comprising contacts within the housing and spaced from one another in a chamber of' the housing, the contacts being resilient and movable toward and from one another to change the space between them, one of the contacts being connected with one of the conductors at the power line end of the switch, and the other contact being connected with the corresponding conductor at the other end of the switch housing, the housing having a key hole opening into the chamber at a location close to the switch, and a removable key which extends through the key hole and into the chamber, the key having a conductor at its inner end extending from a shank of the key and movable into position to bridge the space between the contacts in said chamber when the key is rotated after being inserted through the keyhole, the conductor being of a size which passes through the keyhole whereby the key can be inserted into the housing and removed, the chamber in the housing being oifset differently on opposite sides of the longitudinal axis of the keyhole, and the conductor on the key including'elements extending on opposite sides of the shank at axially spaced locations along the shank corresponding to the ofisets of the chamber, and the end of one of the key elements bearing against a surface of one of the contacts which is shaped to hold the element and key in an angular position in which the key closes the switch.

6. An electrical switch including a housing, conductors in one end of the housing with means for connecting them with wires for leading to a source of power, conductors in the other end of the housing with fastening means for connecting to wires of a drop cord leading to an electrical appliance, spaced contacts within the housing on different sides of a chamber, the contacts being resilient and movable toward and from one another to change the space between them, one of the contacts being connected to a conductor at the power supply end of the housing and the other contact being connected to one of the conductors at the electrical appliance end of the housing, the housing having a key hole opening through at least one side thereof for admitting a key into the chamber between the contacts, a key having a shank which extends through the key hole into the chamber and a conductor element extending from different sides of the shank and slightly longer than the normal spacing of the contacts from one another and adapted to simultaneously reach both of the spaced contacts in the chamber and spread them further apart to obtain pressure against the key when the key is turned into a predetermined angular 7 position for closing the circuit between the spaced contacts, the conductor being of a 'size which passes through the'keyhole whereby the key can be inserted into the housing and removed, the housing being made in two separate halves with depressions therein which form different parts of the switch chamber, and fastening means holding the two halves of the housing together with the sides having the recesses confronting one another so that the recesses form the chamber in the housing, the key hole extending through only one side of the housing and the other side providing an end wall against which a key abuts to limit the extent to which the key can be inserted into the key hole, the depressions which form the chamber being differently located in the different halves of the housing and providing offset portions of the chamber, and the conductor on the key having elements extending from opposite sides of the shank and located in positions to extend into the offset portions of the chamber when the shank is rotated about its axis, one of the contacts in the switch being resilient and having a depression therein for receiving one end of one of the elements of the'key when the key is turned into position to close the switch.

7. An electrical switch including a housing of substantially greater length than its width and thickness, two conductors at one end of the housing for connection with a source of power, two conductors at the other end of the housing for connection with a load, the housing enclosing a switch chamber and having a key hole opening through a side wall of the chamber, two switch elements in the chamber on opposite sides of the key hole'and in position to leave agap between themwhieh can be bridged by a conductor carried at the'inner end of a removable key which is adapted'to be inserted through the key hole and .into'the chamber, each of'the' switch elements-being heldin place in the housing by a longitudinally extending portion which-serves as a spring'means for the switch elements, the switch elements having sloping surfaces thereon for facilitating snap action of the switch .by the operating key, and the elongated portions which serve as spring means extending generally parallel'to one another along a portion of the length of the housing, and one of the elongated portionsbeing connected'with one of'the power line conductors of the switch and the other of the elongated portions being connected with the load conductor at the other end of the housing'butin thesame side of the circuit'as the first elongated portion.

References Cited in the file of this patent UNITED STATES PATENTS 

